Clinical Takeaway
Context
Researchers in the U.K. recently reported results from a large randomized trial of a multicancer screening blood test, which is currently under review by the U.S. FDA. Here, in an industry-sponsored, observational study of the same test in the U.S., 35,000 participants (median age, 64) underwent screening during year 1. Standardized protocols, guided by a positive test’s predicted cancer signal origin, were used for diagnostic testing.
Key Results
- 0.9% of participants had positive tests; 60% of those with positive tests subsequently received diagnoses of cancer.
- Among participants with positive tests, most underwent invasive testing (73%) — usually biopsy or endoscopy — and about half underwent whole-body imaging (magnetic resonance imaging, computed tomography [CT], or positron-emission tomography [PET]/CT). If targeted testing was negative, a PET/CT was performed.
- Median time to diagnostic resolution was ≈1 month for those with cancer and ≈2 months for those without cancer.
Comment
Given that patients are going to be curious about this test and that some patients might want it done despite lack of evidence on its benefit, these data can inform our discussions. About 1 in 100 tests were positive and about half of those were true positives — similar to the results from the randomized U.K. trial. However, in this study, we can see that screening comes at the cost of invasive testing, extensive (and expensive) imaging, and diagnostic uncertainty. We do not know how many of these cancers would have been discovered by other means (e.g., screening, symptoms). My advice to patients: I’m excited about a blood test for cancer, too, but let’s wait until we have more data. This trial is ongoing, so we’ll see results of subsequent testing rounds in future years.